Pick out the incorrect statement

Options

A. `PH_(4)^(+)` ion is tetrahedral like the `NH_(4)^(+)` ion and
is obained when `PH_(3)` is bonded to proton
B. `PH_(4)I` is one of the most stable salts containing
the phosphonium ion. It is also more stable
than ammonium salts
C. `PH_(4)I` is decomposed by water to form `PH_(3)`
D. `PH_(3)` converts silver salts in solution to silver
phosphide, which subsequently reacts to
give free metal

Answer

To solve the question "Pick out the incorrect statement," we will analyze each of the provided statements one by one.

### Step 1: Analyze the First Statement
**Statement 1:** "Ph4 plus ion is tetrahedral like the ammonium ion and is obtained when Ph3 is bonded to a proton."

- **Analysis:** This statement is correct. The phosphonium ion (Ph4+) indeed has a tetrahedral shape, similar to the ammonium ion (NH4+). It is formed when triphenylphosphine (Ph3) bonds with a proton (H+).

### Step 2: Analyze the Second Statement
**Statement 2:** "Ph4I is one of the most stable salts containing the phosphonium ion. It is also more stable than ammonium salts."

- **Analysis:** This statement is incorrect. As we move down the group in the periodic table, the stability of the hydrides decreases. Ph4I (phosphonium iodide) is less stable than ammonium salts due to the larger size of phosphorus compared to nitrogen, which leads to weaker bonds in phosphonium compared to ammonium.

### Step 3: Analyze the Third Statement
**Statement 3:** "Ph4I is decomposed by water to form Ph3."

- **Analysis:** This statement is correct. Ph4I does decompose in the presence of water to produce phosphine (Ph3), iodide ions (I-), and hydronium ions (H3O+).

### Step 4: Analyze the Fourth Statement
**Statement 4:** "Ph3 converts silver salts in solution to silver phosphide."

- **Analysis:** This statement is also correct. Triphenylphosphine (Ph3) reacts with silver salts to form silver phosphide (Ag3P).

### Conclusion
After analyzing all statements, the incorrect statement is:

**Incorrect Statement:** "Ph4I is one of the most stable salts containing the phosphonium ion. It is also more stable than ammonium salts."